Many types of drugs are provided in fluid form, such as a solution or suspension or emulsion of drug in a propellant, an aerosol propellant, and are adapted for oral inhalation by a patient. As one example, a container might contain asthma medicine such as fluticasone propionate. During a typical manufacturing process, the container is sealed by crimping a metering valve onto the neck of the container. The container is then charged through the valve with the aerosol propellant.
In order to deliver the drug to the patient, the container operates in conjunction with an actuator as a system commonly known as a metered dose inhaler (MDI) system. The actuator includes a housing having an open container-loading end and an open mouthpiece. A nozzle element is disposed within the housing and includes a valve stem-receiving bore communicating with a nozzle orifice. The orifice is aimed toward the mouthpiece. In order to receive a properly metered dosage of medicine from the container, the patient installs the container into the actuator through the container-loading end until the valve stem is fitted into the receiving bore of the nozzle element. With the container so installed, the opposite end of the container typically extends to some degree outside the actuator housing. The patient then places the mouthpiece into his or her mouth and actuates the valve. Owing to the design of the valve, the design of the nozzle element and the pressure differential between the interior of the container and the ambient air, a short burst of precisely metered, atomized formulation is thereby delivered to the patient.
FIG. 1 shows a sectional view of one embodiment of a conventional inhaler container 10 (can). The inhaler 10 is comprised of a can 20 and a linear metering valve assembly 30. The metering valve assembly is basically comprised of a valve mechanism 40 with a valve body 90, a valve stem 100, a valve spring 125, a gasket 50, a ferrule 60, and a support ring 70. Further, there is an opening 130 in the valve body 90, through which the drug enters the valve. In FIG. 1 and all following figures, the inhaler container 10 is shown in the operating position, i.e. with the valve directed downwards. As can be seen in FIG. 1 the valve assembly 30 is attached to the container 20 by a crimp 80, i.e. the upper section of the ferrule 60 is crimped in a crimping apparatus so that it closely clasps the lower section of the container 20. Further, the inhaler can 10 is sealed by the upper edge of the container 20 being pressed against the gasket 50 by the crimp 80. A metering chamber 110 is provided in order for the valve to deliver a metered volume upon actuation. In the rest position, a first seal 150 seals of the metered volume from the surrounding atmosphere, and a small gap between the valve stem 100 and a secondary seal 140 allows the content in the can 20 to enter the metered volume. When actuating the valve 30, the valve stem moves further into the valve body 90, first causing a wider section of the valve stem to enter the seal 140 sealing off the metered volume from the interior of the can, where after a stem bore 120 passes the seal 150 into the metered volume and the pressurized aerosol propellant in the metered volume is discharged via the valve stem 100.
Metering valves 30 of linear type dominates the metering valve market and essentially all inhaler actuators are adapted to this type of metering valve. However, this type of valve has a number of drawbacks, such as a relatively high actuation force that is related to the spring 125, the friction between the valve stem and the seals 140 and 150 and the pressure in the can, and that filling of a container involves the step of forcing the drug and propellant mixture through the seals. Furthermore, linear valves are comprised of a relatively large number of parts that have to be made with high accuracy in order for the valve to work properly and not leak.
U.S. Pat. No. 5,772,085 disclose in one embodiment a rotary metering valve, wherein a valve stem is capable of rotary motion. The valve comprises a nozzle block having a wide passage in communication with an aerosol vial. The nozzle block has an outlet passage for discharge of the pressurised aerosol formulation. An elastomeric sealing element is positioned within the nozzle block and is fixed relative to the nozzle block. A chamber is defined by the inside walls of the elastomeric sealing element. A valve stem is mounted within the sealing element and is capable of rotary movement about an axis. The valve stem has a recess with an opening. In the non-dispensing position there is open communication between the passage and the recess allowing free access of aerosol formulation. As the valve stem is rotated, the opening moves out of line with the passage and thus the opening is blocked by the sealing element thereby forming a closed volume within the recess. Further rotation of the valve stem will bring the opening into communication with the discharge passage thereby allowing the contents of the recess to be discharged under the influence of the aerosol propellant. This valve has neutral bias since there is no spring biasing means and the pressure of the aerosol formulation does not exert a bias. In a modification the valve stem comprises a plurality of recesses circumferentially arranged such that they may be sequentially filled and the contents dispensed by further rotation of the valve stem.
This valve, though simple in appearance, is relatively difficult to make leak proof at the high pressures present in the canister and the large area sealing element, and moreover, as it comprises an elastomeric sealing element that surrounds the valve stem, it is relatively complex to assemble. Moreover, in the basic embodiment with one metering chamber in the form of a recess in the valve stem, the stem has to be rotated 180° in order to be actuated, While in the later proposed embodiment with a plurality of recesses, the sealing situation becomes even more critical and the benefit of free flow of the aerosol formulation in the canister discussed in U.S. Pat. No. 5,772,085 will be lost for the filled recesses waiting to be dispensed. Moreover, this valve as well as the conventional linear valve requires use of elastomeric gaskets or seals, which gaskets are in contact with the drug and propellant mixture and therefore must be essentially inert with respect to the drug and propellant mixture. As such valves includes several materials being in direct contact with the drug and propellant mixture, regulatory approvals get more complicated